Method and device for converting hydrogen sulfide into elemental sulfur

ABSTRACT

A process for recovery of hydrogen fluoride comprises contacting a gaseous mixture containing hydrogen fluoride and an organic compound with a solution of an alkali metal fluoride in hydrogen fluoride, separating a gas phase depleted in hydrogen fluoride and containing the organic compound from a liquid phase enriched in hydrogen fluoride, and then recovering the hydrogen fluoride from the liquid phase.

[0001] The invention relates to a process and an apparatus for theconversion of hydrogen sulfide (H₂S) into elemental sulfur (S).

[0002] Sulfur is required in many chemical processes either in elementalform or in the form of sulfuric acid. However, sulfur is highly toxic inthe form of sulfur dioxide (SO₂) or as hydrogen sulfide. Therefore,there are maximum permissible emission limit values for the sulfurcompounds, which are becoming increasingly more stringent worldwide.

[0003] Fossil fuels, such as natural gas, coal, oil sand, oil shale andpetroleum, comprise organic and inorganic sulfur compounds. It isnecessary to remove these sulfur compounds or to convert them intoharmless sulfur compounds. To remove the sulfur compounds from fuels andcombustion products there exists a multiplicity of physical and chemicalconversion processes.

[0004] In the case of solid fuels, the sulfur compounds are absorbedafter the combustion in the power station as sulfur dioxide by a fluegas desulfurization system using milk of lime and converted into calciumsulfite. By oxidation with the residual oxygen present in the exhaustgas, gypsum is formed as end product.

[0005] In the case of liquid fuels, such as diesel fuel or light fueloil, maximum permissible sulfur contents are prescribed. This is becauseflue gas desulfurization after possible consumption in engines, forexample, can no longer be implemented. The desulfurization of thesefuels is carried out in the refineries. The sulfur compounds present inthe crude oil are recovered in the distillate, the heavy oil fractionhaving the highest sulfur concentrations.

[0006] The desulfurization is performed using gaseous hydrogen (H₂). Theorganic sulfur compounds are converted in this case into hydrogensulfide. The hydrogen sulfide, which is present in the gas mixture withhydrogen and other hydrocarbons, is scrubbed out in amine scrubbers asClaus gas or hydrogen sulfide gas at concentrations of up to 90% byvolume of hydrogen sulfide. Hydrogen sulfide is also formed in the sourwater stripping columns. In this case, hydrogen sulfide is present asaqueous condensate and is stripped out as sour water stripper gas (SWSgas) containing up to 50% by volume of hydrogen sulfide. In addition, upto 50% by volume of ammonia (NH₃) can be present, which is formed bydecomposition of organic nitrogen compounds.

[0007] The combustion of coal or heavy oil in power stations in whichthe fuel is gasified in advance under an oxygen deficit also produces ahydrogen-sulfide-containing synthesis gas, which is purified prior tothe combustion.

[0008] Hydrogen sulfide, moreover, occurs at varying concentrations inassociated oil field gas and in natural gas at a content of up to 30% byvolume and in the off-gas from sewage treatment plants at a content ofup to 5% by volume of hydrogen sulfide.

[0009] The industrial utilization of hydrogen sulfide is limited.Therefore, it is first converted into elemental sulfur and then inspecial plants into sulfuric acid. Elemental sulfur is required in therubber industry. Sulfuric acid is used in the chemical industry.

[0010] Direct conversion of sulfuric acid into elemental sulfur ispossible by thermal cleavage of hydrogen sulfide, wet oxidation ofhydrogen sulfide in a liquid (aqueous) phase and dry oxidation ofhydrogen sulfide in the vapor phase.

[0011] The direct conversion process most frequently utilized with over2000 plants worldwide is the Claus process, which was developed as earlyas 1883. This process is based on a dry oxidation process. Amultiplicity of process variants have arisen. All process variants arebased on the same fundamental chemical reactions and on the use of athermal reactor and a catalytic reactor.

[0012] The thermal reactor consists of a combustion chamber having aburner, a waste-heat boiler and a first sulfur condenser. The catalyticreactor is constructed to have two or three stages. The stages each havea heater, a catalyst bed and a sulfur condenser.

[0013] In the combustion chamber and the catalytic reactors, thefundamental chemical reactions below proceed: $\begin{matrix}\begin{matrix}\left. {{1.\quad \text{H}_{2}S} + {{1/2}O_{2}} + {1.88N_{2}}}\rightarrow{{{1/3}{SO}_{2}} + {{2/3}H_{2}S} + {{1/3}H_{2}O} + {1.88N_{2}}} \right. \\\left. {{2.\quad {1/3}{SO}_{2}} + {{2/3}H_{2}S} + {{1/3}H_{2}} + {1.88N_{2}}}\rightarrow{S + {H_{2}O} + {1.88N_{2}}} \right.\end{matrix} \\\left. {{\text{Overall:}H_{2}S} + {1.2O_{2}} + {1.88N_{2}}}\rightarrow{S + {H_{2}O} + {1.88N_{2}}} \right.\end{matrix}$

[0014] The remaining associated gases present due to the process, suchas hydrogen, methane, higher hydrocarbons, ammonia, steam, carbondioxide, react in accordance with their concentrations in a multiplicityof side reactions.

[0015] The actual Claus reaction between sulfur dioxide and hydrogensulfide in which elemental sulfur and steam are formed is reaction 2.This proceeds in the catalyst bed.

[0016] Elemental sulfur is additionally directly produced by the thermalcleavage of hydrogen sulfide into sulfur and water in the combustionchamber:

H₂S→H₂+½S₂  3.

[0017] This reaction is highly endothermic.

[0018] In terms of the process, one third of the amount of hydrogensulfide, usually a mixture of Claus gas and sour water stripper gas, isburnt by the burner substoichiometrically by the combustion air to giveone third of sulfur dioxide. The remaining hydrogen sulfide is thermallycleaved in the combustion chamber into sulfur and hydrogen in thetemperature range between 900° C. and 1300° C. and is catalyticallyconverted at temperatures between 180° C. and 400° C. in the catalyticreactors together with the unburnt hydrogen sulfide to give elementalsulfur and water. The reaction to give sulfur is optimum when thehydrogen sulfide/sulfur dioxide ratio is two to one. However, theoptimum ratio is only reached to an approximation in practice.

[0019] The elemental sulfur formed in the combustion chamber is alreadyseparated off in the liquid state after cooling the process gasdownstream of the waste-heat boiler and in the first sulfur condenser.In the downstream catalytic reactors, the cooled process gas is heatedto the necessary reaction temperature prior to entry into the catalystsby the upstream heaters using high-pressure steam or a thermal oil. Thesulfur formed by the Claus reaction is likewise separated off in theliquid state in the sulfur condensers.

[0020] On account of the varying hydrogen sulfide concentration in thefeedgas, in the conventional Claus processes, there are two mainvariants: the main stream operation for hydrogen sulfide concentrationsabove 50% by volume and the side stream operation for hydrogen sulfideconcentrations between 30% by volume and 50% by volume.

[0021] In the main stream operation, the entire quantity of hydrogensulfide is partially combusted with the combustion air in the combustionchamber. Owing to the thermal cleavage of the hydrogen sulfide in thecombustion chamber, a high proportion of sulfur is already separated offin the first sulfur condenser downstream of the waste-heat boiler. Forhydrogen-sulfide-rich gas, the degree of sulfur conversion in athree-stage Claus process is 96 to 97%.

[0022] Downstream tail gas treatment plants, generally Claus processeshaving a thermal afterburning, then make it possible to comply with theregulatory limit values dependent on the plant capacity.

[0023] In the side stream operation, on account of the low heating valueof the hydrogen sulfide gas, the gas stream is divided. At least onethird of the hydrogen sulfide gas is burnt with the necessary combustionair in the combustion chamber and the resulting sulfur-dioxide-richreaction gas is mixed with the remaining hydrogen sulfide gas upstreamof the first reactor. In this process, no elemental sulfur is formed inthe combustion chamber, since the hydrogen sulfide gas is completelycombusted.

[0024] At hydrogen sulfide concentrations below 30% by volume, even thesidestream operation is no longer usable, on account of the low heatingvalue. The combustion then becomes unstable. Furthermore, the sidestreamoperation generally requires an ammonia-free feedgas. Otherwise, thecatalysts are contaminated by ammonia via the bypass. When ammonia ispresent, for example when sour water stripper gas is used, the sourwater stripper gas must be burnt separately from the Claus gas in thecombustion chamber. These qualities of the feedgas require modifiedvariants of the Claus process.

[0025] The existing Claus plants frequently have an insufficient sulfurcapacity for a production-related increase in refinery capacity, use ofcheaper but higher-sulfur crude oil qualities or for reduced sulfurconcentration limit values in the end product. The term “sulfurcapacity” here means the amount of sulfur produced per unit time.

[0026] In addition to the new construction or conversion of the Clausplant which may be necessary, there is also the possibility of bypassingthe bottleneck in the apparatus by the use of oxygen. In theseprocesses, the combustion air is partly or completely replaced byoxygen. By using oxygen, the combustion temperature is increased and theinert gas content is decreased or eliminated. This means that specificprocess gas volumes and thus the plant pressure drop are decreased. Thusthe throughput of the sour water gas and Claus gas can be increased andlow-hydrogen-sulfide feed gases having a low heating value and highammonia content can also be processed in a main stream reactor. The useof oxygen in Claus plants is currently the state of the art.

[0027] In the processes currently used, the enrichment of combustion airwith oxygen is the easiest to implement. The increase in throughputhydrogen sulfide is proportional to the rate of oxygen fed. The maximumpossible oxygen rate is limited by the permissible operatingtemperatures of the burner, the waste-heat boiler and of the firstreactor.

[0028] Depending on the boiler present, the maximum permissible oxygenconcentration is 27 to 28% by volume, the permissible operatingtemperatures of the burner, the waste-heat boiler and the first reactorbeing limiting. The degree of conversion of sulfur is not increased incomparison with the conventional Claus process.

[0029] In the COPE process, the combustion air is enriched with oxygen,elevated concentrations at up to 100% by volume of oxygen being able tobe achieved. This requires a special burner and an additionalcirculation fan. In this process, the temperature increase in thecombustion chamber and in the waste-heat boiler due to the high oxygenconcentration is compensated for by recirculating cold process gas. Theprocess gas is drawn in downstream of the first sulfur condenser andblown into the combustion chamber through the burners to decrease thetemperature. The higher process gas rates increase the pressure drop inthe combustion chamber and in the waste-heat boiler. In the downstreamcatalytic reactor stages, the pressure drop is lower on account of thereduced process gas rates.

[0030] The Lurgi-oxygen-Claus burner is a burner which can be operatedwith air, with oxygen, or with air and oxygen as oxidation medium. Themaximum possible oxygen concentration is approximately 80% by volume.The Claus gas and the ammonia-containing sour water stripper gas are fedseparately. The sour water stripper gas is burnt together with the fuelgas with air in a central burner muffle. The Claus gas is burnt withoxygen and air as oxidation medium by a plurality of twin-concentricindividual burners which are symmetrically arranged around the burnermuffle. An individual burner consists of a central oxygen nozzle, aconcentric Claus gas nozzle and a twin-concentric air nozzle. Thisarrangement produces individual oxygen/hydrogen sulfide flames which aresurrounded by cold air/hydrogen sulfide flames. This controls thetemperature in the combustion chamber. Recirculation of cold process gasto decrease the temperature is not necessary even at high oxygen rates.

[0031] In the SURE process, oxygen-enriched air or 100% by volume oxygenis likewise used as oxidation medium.

[0032] In the SURE dual combustion process, combustion of the hydrogensulfide is carried out by two combustion chambers which are connected inseries and are each equipped with a waste-heat boiler and a sulfurcondenser. The hydrogen sulfide gas is burnt with a portion of theoxygen in the first combustion chamber, cooled in a waste-heat boiler,transferred by a burner into the second combustion chamber and theamount of remaining oxygen required for the Claus reaction is added.This apportioning likewise controls the temperature in the combustionchambers.

[0033] In the SURE sidestream burner process, a separate combustionchamber is connected upstream of the existing Claus process. Thehydrogen sulfide gas is apportioned between the two combustion chambers.In the first combustion chamber, combustion with oxygen produces sulfurdioxide alone. To control the temperature, downstream of the waste-heatboiler, a partial stream of the cooled sulfur-dioxide-containing partialstream is blown into the actual combustion chamber through a burnertogether with the remaining hydrogen sulfide gas and oxygen in order toset the hydrogen sulfide/sulfur dioxide ratio necessary for the Clausreaction.

[0034] The use of up to 100% by volume oxygen as oxidation medium offersthe greatest potential for increasing the output of the Claus plants.However, for this purpose, not inconsiderable capital expenditure onplant equipment must be made. In all known oxygen-Claus processes, atleast the burners and the combustion chambers must be replaced. Furthercosts arise if, in addition, a recirculated gas fan or a secondcombustion chamber with waste-heat boiler and sulfur condenser arerequired. Furthermore, operating a recirculation fan is not withoutproblems owing to possible sulfur deposits.

[0035] However, the high potential operating capacity which is thenavailable can usually not be exploited, since the downstream systems,the catalytic reactors for example, are a bottleneck. In contrast,oxygen enrichment requires the lowest capital expenditure, but with onlya maximum of 28% by volume of oxygen in the combustion air, it offersthe lowest potential for increase in the efficiency of a Claus plant.

[0036] The object therefore underlying the invention was to overcome thedisadvantages of the prior art and to provide a process and an apparatusby which in particular the operating capacity and the degree ofconversion of hydrogen sulfide to elemental sulfur are improved. Theprocess and the apparatus, furthermore, are to be able to be integratedinto existing Claus plants with comparatively low additionalexpenditure.

[0037] The object is achieved by a process having the features accordingto claim 1 and an apparatus having the features as described in claim16. Preferred developments are specified in the subclaims.

[0038] The process according to the invention has the advantage that thesulfur capacity of Claus plants is increased with the use of oxygen oran oxygen-rich gas, with only low capital costs being necessary.However, at the same time, substantially higher oxygen concentrations orhydrogen sulfide throughputs are possible in comparison with aconventional oxygen enrichment.

[0039] According to the invention, the oxygen is not used solely asoxidation medium as hitherto, but is additionally used to increase themixing energy in order to improve the mixing between oxidizing agent andfeedgas in the existing combustion chamber. By increasing the mixingenergy, the combustion density and thus the throughput of hydrogensulfide can be increased. This is because this integrates, into theexisting combustion chamber, an additional afterburning zone which isproduced by highly turbulent self-priming oxygen jets. The process gaswhich is partially reacted with air or premixed and is exiting from thecombustor or the burner is thus subjected to complete afterburning.Furthermore, the reactions taking place in the combustion chamberproceed closer to the thermodynamic equilibrium. The terms “partialcombustion” and “afterburning” relate to the stoichiometric combustion.

[0040] Instead of technical-grade oxygen which is supplied compressed bypipeline or is taken off at high pressure in the liquid state fromvacuum-insulated containers, oxygen having a purity of 80% by volume to100% by volume oxygen content can also be used. This is preferablyproduced directly on-site by molecular sieve adsorption systems, forexample vacuum swing adsorption systems (VSA) or pressure vacuum swingadsorption systems (PVSA).

[0041] The additional oxygen is, according to the invention, not addedas hitherto via the burner by enriching the combustion air, but ispreferably blown in at high velocity through at least one or amultiplicity of individual nozzles. These are, depending on the existingconstruction of the combustion chamber, installed symmetricallydistributed in the combustion chamber wall in the transition region tothe combustor or downstream of the burner at the beginning of thecombustion chamber.

[0042] The process gas which is exiting from the combustor or the burnerand is substoichiometrically burnt or premixed with the combustion airof the burner is, owing to the intensive mixing with the oxygen,subjected to complete afterburning and the stoichiometric hydrogensulfide/sulfur dioxide ratio of two to one which is required for theClaus reaction is set, the hydrogen sulfide/sulfur dioxide ratio beingmeasured upstream of the tailgas treatment system.

[0043] For intensive mixing, the exit velocities from the individualoxygen nozzles are preferably in a Mach number range between 0.4 and 2.Mach number (Ma) is here taken to mean the ratio of the nozzle exitvelocity to the speed of sound of the gases. On account of therelatively high exit velocity of the oxygen, highly turbulent free jetsare formed which draw in surrounding combustion chamber atmosphere, mixand react with the combustible constituents. The hydrogen sulfide inthis case is burnt to sulfur dioxide.

[0044] At an exit velocity corresponding to a Mach number of one, thatis the speed of sound, for example, on account of the intensive mixing,the stoichiometric hydrogen sulfide/sulfur dioxide ratio of two to oneis established. This means, the oxygen present in the combustion chamberis completely reacted. The complete reaction of the oxygen increases theservice life of the first catalytic reactor. This is because at reactortemperatures of 380° C. to 550° C., the excess oxygen otherwise presentin Claus plants reacts with the sulfur dioxide present to form sulfurtrioxide (SO₃) which reacts with the aluminum oxide catalyst pelletsaccording to the following reaction equation:

Al₂O₃→Al₂SO₄+O₂  4.

[0045] Aluminum sulfate forms, which coats the catalyst surface and thusinactivates the catalyst.

[0046] Furthermore, at oxygen velocities corresponding to a Mach numberof 1, the oxygen nozzles are thermally relieved, since the flames of thehydrogen sulfide/sulfur dioxide free jet diffusion flames do notstabilize on the nozzle, but burn free in the combustion chamber, liftedoff from the nozzle. In addition, the flame routes are thus displacedfrom the oxygen nozzles into the combustion chamber. The absolute oxygenpressure at the nozzle exit necessary for an oxygen velocitycorresponding to a Mach number of 1 should preferably be 1.93 times thepressure prevailing in the combustion chamber (PBRK).

[0047] The angle of inclination of the oxygen injection lances ispreferably 45° to 90° to the direction of flow, the axes of the oxygenjets intersecting the central axis of the combustion chambers. Theoxygen injection lances are advantageously installed into the inner wallof the combustion chambers with the nozzles flush or recessed.

[0048] In the case of burners which produce swirling flames, that meanswhich have a radial velocity and concentration distribution of theindividual gas components on the combustion chamber, the oxygeninjection lances are preferably installed distributed symmetricallyaround the periphery preferably at a distance of approximately 0.25 ofthe combustion chamber diameter, measured from the center of thecombustion chamber. This produces an oxygen swirled flow directedagainst the swirl of the main flame.

[0049] The oxygen injection lances are preferably concentric, the oxygennozzle being surrounded by a ring-gap nozzle. A protective gas having aminimum exit velocity corresponding to a Mach number of 0.2 isadvantageously permanently blown into the combustion chamber through thering-gap nozzle, in order to cool the oxygen nozzle and to protectagainst sulfur diffusing in.

[0050] The protecting gas used is preferably air, nitrogen or carbondioxide.

[0051] Experiments have shown that, using this process, depending on thehydrogen sulfide concentration, equivalent oxygen concentrations (XO₂)of 21% by volume to 40% by volume of oxygen can be achieved. Theequivalent oxygen concentration is described here by the equation

(XO₂)=0 ₂ total/(air+O₂ additional).

[0052] The rates of Claus gas and sour water stripper gas are increasedin accordance with the oxygen supply.

EXAMPLES

[0053] The examples below show that the temperature in the combustionchamber increases on account of the high equivalent oxygen concentrationand combustion density. More steam is produced in the waste-heat boileron account of the higher amount of waste heat (see table). ExampleExample Example 1 2 3 Claus gas kg/h 442 603 706 SWS gas kg/h 240 259246 Air, total kg/h 1515 1222 797 Oxygen kg/h 0 71 146 Combustionchamber temp. ° C. 1213 1331 1415 Waste-heat boiler temp. ° C. 597 617641 Burner temperature ° C. 297 259 268 Reactor temp. R1 ° C. 355 387395 H₂S/SO₂ ratio 2.08 2.01 2.01 Sulfur capacity % 100 126 142

[0054] In the event of an increase of the permissible combustion chambertemperature of 1500° C., the equivalent oxygen concentration can beincreased to at least 40% by volume. Since heat and mass are exchangedequally rapidly, the temperature in the combustion chamber is evened outat a higher level as a result of the intensive mixing and the heattransfer to the combustion chamber wall is improved. This means that theamount of heat released to the surroundings via the combustion chamberwall is greater. The waste-heat boiler is thermally relieved. Thetemperatures at the burner and in the combustor do not increase.

[0055] The process causes the temperatures to increase due to the highersulfur conversion in the catalytic reactor, with the permissibleoperating temperature of the catalyst of up to 650° C. being able to beexploited. The high combustion temperatures when oxygen is used havebeneficial effect on the thermal cleavage and complete combustion ofhigher hydrocarbons and ammonia, in which case, in particular, a minimumtemperature of 1350° C. should be maintained for complete cleavage andcombustion of ammonia. Owing to the lack of nitrogen ballast, at anequivalent oxygen concentration of 40% by volume, the concentration ofhydrogen sulfide gas in the gas mixture used can be decreased to 20% byvolume of hydrogen sulfide.

[0056] The invention is now described in more detail with reference tothe drawings (FIGS. 1 to 3).

[0057] FIGS. 1 to 3 show a burner and the section connected thereto ofthe combustion chamber of a Claus plant, the burner shown in FIG. 1 andFIG. 2 additionally having a combustor.

[0058]FIG. 1 shows the burner (1) to which are fed via a 3-foldconcentric tube (2) having an inner pilot tube (3) a fuel gas via themiddle tube (4) and the Claus/SWS gas via the outer tube (5). Air ispassed into the burner (1) via line (6). The combustion takes place inthe combustor (7) and combustion chamber (8) connected thereto.According to the invention, oxygen is introduced at high velocity intothe combustion chamber via a nozzle (9). In addition, it is shown herethat the lance for introducing the oxygen (10) consists in its frontregion of a twin-concentric tube, the oxygen being introduced by theinner tube (11) and a protecting gas to cool the nozzle (9) beingintroduced via the outer tube (12). The angle “β” here denotes the angleof inclination of the oxygen lance in relation to the direction of flow(R). The angle “β” according to the invention is in the range from 45°(β) and 90° (β′). Combustor (7) and combustion chamber (8) are here aone-piece construction.

[0059]FIG. 2 shows a similar embodiment as FIG. 1, combustor (7) andcombustion chamber (8) being separate from one another. The burner (1)has a three-fold concentric tube (2) having an inner tube (3) for pilotgas, a middle tube (4) for fuel gas and an outer tube (5) for Claus/SWSgas. Air is fed via a line (6). A combustor (7) is arranged upstream ofthe combustion chamber (8). Oxygen and a protecting gas are fed via atwin-concentric tube, the oxygen being conducted in the inner tube (11)and the protecting gas in the outer tube (12). The oxygen lance is at anangle β to β′ (45° to 90°) to the direction of flow (R).

[0060] In FIG. 3, the combustion chamber (8) is directly connected tothe burner (1) of the Claus plant. In this embodiment, the pilot gas isintroduced into the burner via a separate tube (13).

1. A process for producing elemental sulfur by combustion of hydrogensulfide or a hydrogen-sulfide-containing gas, in particular a Clausprocess, in which the hydrogen sulfide or thehydrogen-sulfide-containing gas is, via a first device, partiallycombusted in a burner in a combustion chamber with addition of air andoxidation medium, the oxygen or the oxygen-containing gas being fed tothe combustion chamber by at least one second additional device of thecombustion chamber, by which means the hydrogen sulfide or thehydrogen-sulfide-containing gas is subjected to afterburning and is thenfed to a waste-heat boiler and thereafter to one or more reactors. 2.The process as claimed in claim 1, in which the oxygen-containing gashas a purity of 80% by volume to 100% by volume of oxygen.
 3. Theprocess as claimed in claim 1 or 2, in which the oxygen or theoxygen-containing gas is blown in by one or a multiplicity of individualnozzles.
 4. The process as claimed in one of claims 1 to 3, in which theintake velocity of the oxygen or the oxygen-containing gas into thecombustion chamber is in the range of a Mach number between 0.4 and 2,as a result of which the mixing between the oxygen, the combustion airand the hydrogen-sulfide-containing process gas is increased on accountof high turbulence.
 5. The process as claimed in one of claims 1 to 4,in which the oxygen or the oxygen-containing gas enters into thecombustion chamber at an angle of 45° to 90° measured in the directionof flow.
 6. The process as claimed in one of claims 1 to 5, in which, inthe case of a process having swirl of the main flame in the combustionchamber, a swirl flow of the oxygen or oxygen-containing gas is producedwhich is directed against the swirl of the main flame.
 7. The process asclaimed in one of claims 1 to 6, in which the entry point of the oxygenor the oxygen-containing gas into the combustion chamber is cooled andis protected against sulfur diffusing in.
 8. The process as claimed inclaim 7, in which, for cooling, in addition, a protecting gas is fed tothe combustion chamber in the region of the point of entry of the oxygenor the oxygen-containing gas into the combustion chamber.
 9. The processas claimed in claim 8, in which air, nitrogen or carbon dioxide is usedas protecting gas.
 10. The process as claimed in claim 8 or 9, in whichthe intake velocity of the protective gas into the combustion chamber isat least Mach number 0.2, as a result of which the turbulent mixturebetween the oxygen, the combustion air and thehydrogen-sulfide-containing process gas is additionally increased. 11.The process as claimed in one of claims 1 to 10, in which the rate ofoxygen fed is controlled in accordance with the stoichiometry of theClaus reaction in such a manner that the oxygen and the combustion airreact completely with hydrogen sulfide and the other combustible gasesso that no excess oxygen is present downstream of the combustionchamber.
 12. The process as claimed in one of claims 1 to 11, in whichthe rate of oxygen fed is controlled in accordance with thestoichiometry of the Claus reaction in such a manner that the hydrogensulfide/sulfur dioxide ratio corresponds to the theoretical value
 2. 13.The process as claimed in one of claims 1 to 12, in which the rate ofoxygen fed is controlled in accordance with the stoichiometry of theClause reaction in such a manner that the maximum temperatures in theburner/combustor are 250° C./1200° C. and the maximum temperature in thecombustion chamber is 1500° C., so that the heat transfer to thecombustion chamber wall is improved and the maximum temperature in thewaste-heat boiler is 670° C.
 14. The process as claimed in one of claims1 to 13, in which the concentration of oxygen in the oxidation medium(equivalent oxygen concentration) is between 21 and 40% by volume. 15.The process as claimed in one of claims 1 to 14, in which theconcentration of the hydrogen sulfide in the feed gas is at least 20% byvolume.
 16. An apparatus for producing elemental sulfur by combustion ofhydrogen sulfide or a hydrogen-sulfide-containing gas, in particular aClaus plant, in which the hydrogen sulfide or thehydrogen-sulfide-containing gas is partially combusted in a burnerhaving a combustion chamber, with addition of air, oxygen or anoxygen-containing gas being fed to the combustion chamber via at leastone additional nozzle of the combustion chamber, as a result of whichthe hydrogen sulfide or the hydrogen-sulfide-containing gas is subjectedto afterburning and is then fed to a waste-heat boiler and thereafter toone or more reactors.
 17. An apparatus as claimed in claim 16, in whichthe nozzles, in the installed state, are arranged flush or recessed inthe refractory brick lining of the combustion chamber.
 18. The apparatusas claimed in claim 16 or 17, in which, in the case of a process havinga swirled main flame in the combustion chamber the nozzle(s) areinstalled tangentially at a distance which corresponds to 0.25 times thediameter of the combustion chamber, measured from the center of thecombustion chamber, so that a swirl flow of the oxygen oroxygen-containing gas is produced which is directed against the swirl ofthe main flame.
 19. An apparatus as claimed in one of claims 16 to 18,in which, in the case of a process having a swirled main flame in thecombustion chamber, the nozzle(s) are installed tangentially at adistance corresponding to 0.25 times the diameter of the combustionchamber, measured from the center of the combustion chamber, so that aswirl flow of the oxygen or oxygen-containing gas is produced, which isdirected against the swirl of the main flame.
 20. The apparatus asclaimed in one of claims 16 to 19, in which the oxygen or theoxygen-containing gas is blown in via at least one or a multiplicity ofnozzles which are installed symmetrically in the combustion chamber wallin the transition area to the combustor.
 21. The apparatus as claimed inone of claims 16 to 20, in which a ring-gap nozzle is arranged aroundthe nozzles for blowing in the oxygen or the oxygen-containing gas,through which ring-gap nozzle a protective gas is additionally blown in.